I have this problem too, tried to used modded launcher too, or game without any mods, but nothing worked.
From my perspective the problem has really trivial cause. After clicking "Edit in game" button, Create a World Tool tries to open the game directly, by skipping the launcher. Origin had added that program to exceptions and allowed it to open the game by itself. EA app doesn't have this program in exceptions and doesn't allow it. When I try to use Edit in Game mode, CAW tries to open the game and skip the launcher, by then EA app interrupts it, stops the process, and then launch the game by it's own basis just regularly opening the launcher. So the right process which was supposed to happen, was just broken in meanwhile.
I don't know if adding this program to exceptions in EA app resolve all the problems, but it's worth to try at first place. Don't know how if EA app and Origin are similar in coding, or are on competely different engines, but developers should check out how it was resolver in case of Create a World Tool. Cause Origin allowed to use it and launch the game with it's own method.
CAW is located usually in:
C:\Program Files (x86)\Electronic Arts\The Sims 3 Create a World Tool
but for odd reason, folders are named in different way for each language version. For example, for polish language version the path looks like this:
C:\Program Files (x86)\Electronic Arts\Narzędzie The Sims 3 Stwórz świat
...
But the thing that doesn't change, is inside of these folders. Create a World Tool is simply called "CAW.exe" and as I said, it's located in these path above. Maybe players playing in other language versions will paste the exact location in their case too. What I try to say, is that it's worth to start here and add "CAW.exe" to exeptions, so EA app would allow it to open the game on it's own way (without the launcher), to simply edit the worlds and let simmers end their long term projects in game.
Hope I can mention there EA's employees @EA_Cade